The invention relates generally to marking devices and more specifically to markers having a marking fluid reservoir of absorbent material. Such devices generally consist of an absorbent reservoir, a fibrous, absorbent writing tip and a holder, supporting the writing tip in contact with the reservoir. The reservoir usually contains a voltatile marking fluid or ink (interchangeable terms). Markers of this type are made with a variety of marking tip shapes and ink shades. Narrow, "fine-line", writing tips are used as fountain pens for longhand writing, drawing, and applying cosmetics. Wider tips with dark ink shades may be used for package labelling and various forms of artwork. Wider tips in combination with pastel inks (yellow, pink, etc.) are used by students for "highlighting." "Highlighting" consists of covering an important word, sentence or paragraph with a coating of pastel ink to make it stand out, or emphasize it. A recent modification of this basic design is the rolling-ball type marker where a wick is used to transport marking fluid from a reservoir to a rotatably mounted ball.
The vast majority of such markers are designed to be filled with ink just once at the factory. When the ink supply runs out the marker is discarded. A problem with such single-filling markers is that the concentration of ink in the reservoir varies from a maximum at the time of purchase to a minimum when the pen is discarded. As a result the concentration of ink in the marking tips, and the amount or density of ink applied to the writing surface also vary during the life of the marker. When a newly purchased marker is used, a very heavy, dense ink coating will be applied. This will sometimes soak through the page, or leave "puddles" or smudges at the end of a line. For an intermediate period a desired amount of ink will be applied. But then as the ink supply is depleted the marker will leave a coating which is undesirably thin or faint. Similar problems can result with markers used for other purposes. Presently available markers have no means to prevent the density of ink application from varying along with changes in the ink concentration in their reservoir during the life of the markers.